Lobbyists representing the Saudi government reserved blocks of rooms at President Trump’s Washington, D.C., hotel within a month of Trump’s election in 2016 — paying for an estimated 500 nights at the luxury hotel in just three months, according to organizers of the trips and documents obtained by The Washington Post.

At the time, these lobbyists were reserving large numbers of D.C.-area hotel rooms as part of an unorthodox campaign that offered U.S. military veterans a free trip to Washington — then sent them to Capitol Hill to lobby against a law the Saudis opposed, according to veterans and organizers.

At first, lobbyists for the Saudis put the veterans up in Northern Virginia. Then, in December 2016, they switched most of their business to the Trump International Hotel in downtown Washington. In all, the lobbyists spent more than $270,000 to house six groups of visiting veterans at the Trump hotel, which Trump still owns.

Those bookings have fueled a pair of federal lawsuits alleging Trump violated the Constitution by taking improper payments from foreign governments.

During this period, records show, the average nightly rate at the hotel was $768. The lobbyists who ran the trips say they chose Trump’s hotel strictly because it offered a discount from that rate and had rooms available, not to curry favor with Trump.

“Absolutely not. It had nothing to do with that. Not one bit,” said Michael Gibson, a Maryland-based political operative who helped organize the trips.

Some of the veterans who stayed at Trump’s hotel say they were kept in the dark about the Saudis’ role in the trips. Now, they wonder if they were used twice over: not just to deliver someone else’s message to Congress, but also to deliver business to the Trump Organization.

“It made all the sense in the world, when we found out that the Saudis had paid for it,” said Henry Garcia, a Navy veteran from San Antonio who went on three trips. He said the organizers never said anything about Saudi Arabia when they invited him.

He believed the trips were organized by other veterans, but that puzzled him, because this group spent money like no veterans group he had ever worked with. There were private hotel rooms, open bars, free dinners. Then, Garcia said, one of the organizers who had been drinking minibar champagne mentioned a Saudi prince.

The Saudi Embassy did not respond to questions for this report. Trump hotel executives, speaking on the condition of anonymity to discuss their clients, said they were unaware at the time that Saudi Arabia was ultimately footing the bill and declined to comment on the rates they offer to guests.

The existence of the Saudi-funded stays at Trump’s hotel was reported by several news outlets last year. But reviews of emails, agendas and disclosure forms from the Saudis’ lobbyists and interviews this fall with two dozen veterans provide far more detail about the extent of the trips and the organizers’ interactions with veterans than have previously been reported.

That reporting showed a total of six trips, during which the groups grew larger after the initial visit and the stays increased over time. The Post estimated the Saudi government paid for more than 500 nights in Trump hotel rooms, based on planning documents and agendas given to the veterans and conversations with organizers.

These transactions have become ammunition for plaintiffs in two lawsuits alleging that Trump violated the Constitution’s foreign emoluments clause by taking payments from foreign governments. On Tuesday, the attorneys general in Maryland and the District subpoenaed 13 Trump business entities and 18 competing businesses, largely in search of records of foreign spending at the hotel.

“Foreign countries understand that they can curry favor with the president by patronizing his businesses,” said Rep. Adam B. Schiff (D-Calif.), who will lead the House Intelligence Committee next year. “It presents a real problem, in that it may work.” The White House declined to comment.

When these trips began, in late 2016, the Saudi government was on a losing streak in Washington.

In late September, Congress had overridden a veto from President Barack Obama and passed a law the Saudis vehemently opposed: the Justice Against Sponsors of Terrorism Act, called JASTA. The new law, backed by the families of Sept. 11 victims, opened the door to costly litigation alleging that the Saudi government bore some blame. Of the 19 hijackers involved in the attacks, 15 were Saudi citizens.

In response, the Saudis tried something new. To battle one of America’s most revered groups — the Sept. 11 families — they recruited allies from another.

They went looking for veterans.

“Welcome Home Brother!” wrote Jason E. Johns, an Army veteran and Wisconsin lobbyist, to several veterans in December 2016, according to identical emails two veterans shared with The Post. Johns invited the veterans, whom he did not know personally, on a trip to “storm the Hill” to lobby against the law.

“Lodging at the Trump International Hotel, all expense paid,” Johns wrote in the emails. Johns’s email signature said he was with “N.M.L.B. Veterans Advocacy Group,” which is Johns’s law firm in Madison, Wis.

According to filings with the Justice Department, Johns was actually making the overtures on behalf of theSaudi government. The Saudis’ longtime lobbyist, Qorvis, was paying Gibson, who in turn was paying Johns.

The first trip Johns organized, in mid-November 2016, was small and short: about 22 veterans, staying two nights at the Westin inCrystal City, Va. — on the other side of the Potomac River, separated from Capitol Hill by four miles and one big traffic jam. Gibson — who helped organized the trips — said another fly-in was held at the Westin later the same month.

Then, on Dec. 2, 2016, Gibson said he was told by Qorvis to organize another visit on very short notice — with the attendees to arrive in just a few days. Gibson said the Westin was booked. So were many other hotels he tried.

“I just out of the blue decided, ‘Why not call the Trump hotel?’ ” he said. “I said I was representing a client, a group of veterans . . . Did they offer any discounts for veterans? And they said yes, they did have availability.” They also offered a lower rate, he said.

After that trip, Gibson said, Qorvis asked him to schedule more trips for 2017. It didn’t tell him to go back to the Trump hotel. But the first trip had gone well. So he did.

In all, there were five more trips in January and February, according to documents and interviews. The number of attendees rose to 50 on one trip in late January, and the trips extended to three nights, according to agendas sent to veterans. That also was the clients’ call. Gibson said he never told any Trump hotel staff that the Saudis were paying: “I did all this on my corporate credit card for my client, who was Qorvis, and said I was bringing a group of veterans to work on legislation.”

Veterans who attended these trips said a few things surprised them.

One was how good their group seemed to be at spending money.

“We’ve done hundreds of veterans events, and we’ve stayed in Holiday Inns and eaten Ritz Crackers and lemonade. And we’re staying in this hotel that costs $500 a night,” said Dan Cord, a Marine veteran. “I’d never seen anything like this. They were like, ‘That’s what’s so cool! Drink on us.’ ”

Each trip included one, and sometimes two, dinners in a Trump hotel banquet room. There was usually an open bar in the room, veterans said, and it was always supposed to end at a certain hour — but often, they said, Johns would theatrically declare an extension.

“He’d be like, ‘You know what, just put it on for another hour!” said Scott Bartels, an Army veteran from Wisconsin who went on three trips.

Another surprise, veterans said, was how bad their group seemed to be at lobbying.

Veterans said they were told that the new law might cause other countries to retaliate and might lead to U.S. veterans being prosecuted overseas for what their units had done in war. They were given a few fact sheets — including one with small print at the bottom, reading “This is distributed by Qorvis MSLGROUP on behalf of the Royal Embassy of Saudi Arabia.”

But they said they weren’t given detailed briefings about how the law ought to be amended, or policy briefings to leave behind for legislators to study.

The timing also was odd. They returned five times in January and February, when the issue was largely dormant and Washington was distracted by a new president’s inauguration. They were sent, again and again, for dead-end meetings with legislators who had made up their minds.

“The fourth time I saw Grassley’s guy, he was like, ‘Hey, what [else] is going on?’ We didn’t even talk about the bill,” said Robert Suesakul, an Army veteran from Iowa, about his fourth visit to the office of Sen. Charles E. Grassley (R-Iowa). It had been clear after the first trip that Grassley wasn’t interested in amending the bill. “It didn’t make sense hitting these guys a fourth time.”

Another problem: In some cases, congressional staffers confronted them because they knew who was funding these trips.

Even if the veterans did not.

“We’d walk in there, and they’d go, ‘Are you the veterans that are getting bribed?’ ” Suesakul said.

In a phone interview, Johns said it was disappointing to hear veterans say they were “duped” and that he had always made clear, at the opening night’s dinner, that the Saudi government was paying. He said the veterans in attendance were all told that if they didn’t like it, they could go home.

“I said, ‘Look, I’m a fellow vet, and I am working with a PR firm here, and Saudi Arabia funded” the trip, Johns said.

But another organizer, Army veteran Dustin Tinsley, didn’t remember Johns telling everyone about the Saudi involvement. He did say he felt veterans should have done their own research or asked.

“When I was asked directly, ‘Is Saudi Arabia paying for this?’ I would say yes, and out of [all of them] not a single one of them said, ‘I don’t want to be a part of this,’ ” Tinsley said.

Several veterans disputed Johns’s account, saying they were not told of the source of the funding — or that the news had only slipped out later, after repeated questioning or strong drink.

“One of the guys had a little too much to drink,” said Gary Ard, a Navy veteran from Texas, describing an encounter with one of Johns’s aides after the aide had been drinking at the Trump hotel. “He kind of raises up his hands, and he says, ‘Thank you, Saudi prince!’ ”

Ard quit going after two trips. He said he felt guilty, for having unwittingly gathered political intelligence for a foreign power.

“We’re taking that heart-to-heart conversation [with legislators], writing it down, and giving it to a group of people whom I don’t know,” Ard said. “And my fear in that is we’re going to create a pool of insight to what congressmen, what senators can be approached, and what their mind-sets are. And that’s completely wrong.”

The last trip to the Trump hotel was in mid-February 2017, after the first news reports outed Johns as a Saudi contractor. Johns himself said he wasn’t sure how much the trips had cost: The bills for the hotel rooms didn’t go to him, and he never saw how much the rooms cost.

In a filing with the Justice Department — required of U.S. firms working as agents for foreign powers — Qorvis said it had spent $190,000 on lodging at the Trump hotel, and another $82,000 on catering and parking.

Since February 2017, Saudi customers have boosted the bottom line at two other Trump hotels. In Chicago, the Trump hotel’s internal statistics showed a sharp uptick in customers from Saudi Arabia after Trump took office. In New York this year, the general manager of Trump’s hotel at Central Park said a single stay by some Saudi customers — who were traveling with Crown Prince Mohammed bin Salman — was so lucrative it helped the hotel turn a profit for the quarter.